A gas generator that works to expand and inflate the airbag rapidly to protect a vehicle occupant from the impact at a car collision is built in an airbag module mounted in a steering wheel and the like. The gas generator generates a large amount of gas rapidly by burning the gas generants by flames of ignitor device ignited by the application of electric power.
The conventional gas generator has the mode of expanding and inflating the airbag rapidly at any time that the car collision happens, irrespective of a seating position of a vehicle occupant (a normal seating position or an abnormal seating position such as a stoop-shouldered position, etc.). This may cause the problem that when the vehicle occupant takes the abnormal seating position in proximity of the steering wheel and the like, the airbag cannot serve its original function of protecting the vehicle occupant.
For solving this problem, there has been proposed and developed the so-called soft inflation technique which is applied to the gas generator used for expanding and inflating the passenger's airbag. The proposed gas generator is so designed that an elongated cylindrical housing is partitioned into two combustion chambers and also the gas generants in the respective combustion chambers are burnt independently of each other by the two ignitor devices. The ignitor devices are fixed to the housing at both axial ends thereof.
The ignitor devices are operated in such a time difference that, in the initial stage of inflation, the airbag is expanded and inflated moderately by a small amount of gas generated from a first combustion chamber and then is expanded and inflated rapidly by a large amount of gas generated in the respective combustion chambers. This can provide a controlled expansion and inflation of the airbag.
It is conceivable that this soft Inflation technique is applied to the gas generator used to expand and inflate the driver's seat airbag.
As the gas generator for the driver's seat airbag is usually built in a narrow space of the steering wheel, it is required to have a short cylindrical housing. In addition, as the airbag is also mounted in that narrow space of the steering wheel, the airbag is required so as to cover the housing of the gas generator at one axial end thereof. For this reason, the gas generator for the driver's seat airbag adopts the structure that the ignitor device is mounted in the housing at the other axial end thereof to be in the opposite side to the airbag.
As a result of this, when the soft inflation technique is applied to the gas generator for the driver's seat airbag, the gas generator for the driver's seat airbag adopts the structure that the housing is partitioned into two combustion chambers and also two ignitor devices are mounted in the housing at the other axial end thereof. In this structure, when the ignitor devices are energized to ignite with an adequate time difference, the airbag is expanded and inflated moderately by a small amount of gas generated from the first combustion chamber in the initial state of inflation and then expanded and inflated rapidly by a large amount of gas generated in the respective combustion chambers.
In the application of the soft inflation technique to the gas generator for the driver's seat airbag, one or two or more of the ignitor devices must be offset from the axis of the housing in order to be mounted in the housing at the other end thereof.
As a result of this, local combustion stemming from the eccentrically disposed ignitor device is produced in the combustion chamber in which the eccentrically disposed ignitor device is/are fitted. This causes possible problems that the gas cannot be uniformly generated all around the circumference of the housing and thus cannot be uniformly discharged into the airbag, then leading to the partial expansion and inflation of the airbag, and as such may spoil the original function of the airbag of protecting the vehicle occupant.
It is the object of the present invention to provide a gas generator that enables flames of the ignitor device to be propagated in the circumferential direction and radial direction of the housing via enhancer device, so as to instantaneously transfer the burning of the gas generants to the collective burning of the same, whereby the generated gas is uniformly discharged into the airbag.